George Osborne today admitted he cannot stop oil companies putting up the price of fuel despite the duty cut announced in his Budget.

But the Chancellor said he would be watching "like a hawk" to make sure there was "no funny business".

Mr Osborne lopped 1p a litre off fuel duty in yesterday's budget and introduced a Fair Fuel Stabiliser, funded by £2 billion of new taxes on the windfall profits of oil companies due to record global prices.

He told ITV's Daybreak: "We will be watching like a hawk to make sure that motorists get the benefit of the budget changes and make sure that there's no funny business."

Asked if there was a mechanism to stop the oil companies putting prices up, he said: "I'm not in control of the world's oil price unfortunately.

"What I am in control of are the taxes that go onto oil in Britain, in other words the duty that gets levied at the petrol station."

He continued: "I'm not pretending that this is going to transform the situation over night for families who are feeling the squeeze, but it helps."

David Cameron and Nick Clegg will hit the road together today as they try to reinforce Mr Osborne's message that the coalition is "putting fuel into the tank of the British economy".

The Prime Minister and his deputy will announce the first enterprise zones designed to kickstart regional growth as they promote the Budget to the country.

Mr Cameron and Mr Clegg will disclose the locations of the first batch of a planned 21 enterprise zones meant to help the private sector excel as public spending is cut by £81 billion over the next four years.

Mr Osborne said the first 10 zones would be in "urban areas of highest need but also potential".

In them, businesses will get special allowances, including discounts on rates of up to 100%, and superfast broadband. Local authorities will be asked to reduce planning restrictions in return for keeping all growth in business rates.

Mr Osborne's second Budget was delivered against a backdrop of deteriorating growth and borrowing figures, which Labour claimed were an indication that his cuts programme is harming the British economy.

The independent Office for Budget Responsibility has downgraded its GDP growth forecast from 2.1% to 1.7% this year and from 2.6% to 2.5% in 2012.

While the OBR predicted stronger growth in subsequent years, it warned: "We expect this recovery to be weaker than the recoveries of the 1980s and 1990s."

The Institute for Fiscal Studies said Mr Osborne was especially reliant on a growth bounce-back from 2013 given the forecast downgrade.

The IFS said if the OBR had overestimated output by as little as 1.5% it would breach the Chancellor's fiscal plans.

Director Paul Johnson said: "Given these forecasts it is clear why a Chancellor sticking to his plans did not feel able to engage in a net giveaway.

"Going forward he is going to be uncomfortably dependent on the judgments that the (independent) OBR makes over the (unobservable) potential output of the economy."

The shift to uprate tax allowances and thresholds in line with the Consumer Prices Index (CPI) rather than the usually higher Retail Prices Index (RPI) would increase "fiscal drag", the IFS added.